I hope you and that proposal will consider allowing the creation of default member functions of classes that have const members and references by taking advantage of "transparently replaceable".

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c12-dont-make-data-members-const-or-references-in-a-copyable-or-movable-type
https://stackoverflow.com/questions/4136156/const-member-and-assignment-operator-how-to-avoid-the-undefined-behavior
https://timsong-cpp.github.io/cppwp/n4861/basic.life#8




On Sun, Jun 22, 2025 at 6:31 AM Matthew Taylor via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
I believe this exact topic came under discussion in EWG last week as part of the discussion on potential extensions to P2034 Partially Mutable Lambda Captures (https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2034r4.pdf). Stronger consensus was found to see a version of the paper with extensions such as const-ref-capture.

Perhaps it would be a good idea to reach out to the authors of P2034 to see if they would collaborate on designing such extensions.

FWIW to answer your question about other qualifiers - I can see the symmetry argument for volatile, but I'd want to see a really compelling use-case to approve adding more volatile to the language.

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